The invention relates to an eccentric gear transmission for stepping up the rotary motion of adjusting motors.
For reducing the rpm of adjusting motors, in which the rotary speed of the armature is approximately 7000 rpm, worm gears are as a rule employed. These worm gears, which are driven by electric motors, are distinguished by having self-inhibition from the power takeoff side. Because of the high step-up ratio required to achieve adequate torques, for instance for a power window or power sunroof drive unit in a motor vehicle, the external dimensions of an adjusting motor comprising a motor and side-by-side gears are considerable.
The eccentric gear transmission of the invention having the characteristics of the main claim has the advantage of very compact dimensions yet it has self-inhibition and a simple design. Compared with the known worm gears, the eccentric gear transmission is comparatively free of tolerance problems, since all the rotating parts are disposed on one shaft.
An essential component of the eccentric gear transmission is an eccentric wheel, which by its construction can execute two different motions. One of these is rolling along a set of external teeth of a driver, which leads to a circular motion about a pivot point that is eccentric to the axis of the eccentric wheel (xe2x80x9cswash motionxe2x80x9d), and the other is a rotation about itself. The rotation about itself is undesired and is prevented by guide elements on the eccentric wheel that protrude into corresponding receptacles of a housing part solidly joined to the housing.
The circular motion of the eccentric wheel can be split into two linear motions perpendicular to one another. In the transmission of the invention, these two linear motion components are absorbed by a single part, while in conventional versions they are absorbed by two separate parts. Because of the one-piece embodiment of the housing part that absorbs the circular motions of the eccentric wheel, production costs on the one hand and the effort and expense of assembly on the other are reduced. Both effects are advantageous.
The particular advantage of the one-piece version of the housing part and the vibratable disposition of the receptacles is that the interaction between the guide elements of the eccentric wheel and the receptacles of the housing part takes place entirely without friction and thus without wear. This guarantees a correspondingly long expected life of the eccentric gear transmission of the invention.
Advantageous refinements of the eccentric gear transmission defined by the main claim are possible with the characteristics recited in the dependent claims.
For instance, the housing part is advantageously made up of three regions joined together and has an inner region with receptacles, a middle region, and an outer region joined solidly to the housing; the inner region and the middle region are disposed vibratably relative to the outer region. The cooperation of the guide elements, mounted on the eccentric wheel, with the receptacles on the inner region of the housing part brings about the advantageous guidance of the eccentric wheel.
As a result of joining the inner region to the middle region and the middle region to the outer region via deformable regions, the advantage is obtained that the circular motion of the eccentric wheel about a center position, which is required for operating the eccentric gear transmission, remains assured.
The advantage of the one-piece design mentioned at the outset is obtained structurally by embodying the deformable regions by means of recesses. Thus the complete housing part can be produced in a suitable shape as a single part by injection molding.
An elongated extension of the deformable regions is advantageous because then, with minimal stress on the material, the requisite deformation or deflection of the deformable regions remains assured.
If the deformable regions between the inner region and the middle region and the deformable regions between the middle region and the outer region are disposed crosswise to one another, the advantage is obtained that the circular motion of the eccentric wheel is separated exactly into the two linear components, perpendicular to one another, of this motion. The resultant forces are thus distributed uniformly to the housing part and to the deformable regions.
By narrowed portions on the ends of the deformable regions, their elasticity or spring-constants can be adjusted to suit existing requirements.
In a further advantageous version of the invention, the housing part is made up of only two regions joined together, and it has an inner region and an outer region that is solidly joined to the housing; in this case, the inner region is vibratable relative to the outer region, and the receptacles are vibratable relative to the inner region.
By joining the inner region to the outer region and by joining the receptacles to the inner region via deformable regions, the advantage is obtained, precisely as in the first variant, that the circular motion of the eccentric wheel about a center position, which is required for the operation of an eccentric gear transmission, remains assured.
It is especially advantageous in this respect that all of the deformable regions are of equal length and are equally far away from the center point and are thus exposed to an equal stress.
The formation of the deformable regions by recesses, the elongated extension, and the disposition of the deformable regions that joined to the receptacles crosswise to the regions that are not joined to the receptacles all produce the aforementioned advantages.